Head to head
Which one will break you first?
Two fingerprints on one grid. Both are scored through your profile, so this answers the question for you rather than for the average player.
Age of Empires II: Definitive Edition is the harder of the two for you, by 1.2 points. The gap is widest on grind, where Age of Empires II: Definitive Edition asks considerably more than Metal Gear Solid Δ: Snake Eater. If you want the gentler run, start with Metal Gear Solid Δ: Snake Eater.
Axis by axis, biggest gap first
METAL GEAR SOLID Δ: SNAKE EATER
Systems difficulty rather than reflex difficulty. Camouflage, stamina, wounds and food are four meters that all decay, and the game never tells you which one is currently the reason you keep being spotted.
Real resistance. Expect to work for it.
AGE OF EMPIRES II: DEFINITIVE EDITION
Build orders are the curve, and the campaigns teach almost none of what the game actually asks for. The hard AI does not forget its economy while it fights.
Sustained pressure. Progress is earned.